Clear-cut evidence having been obtained that the hardy, nonpathogenic lower trypanosomatid Leptomonas from Dysdercus is much more sensitive to several standard trypanocides and leishmanicides (ethidium, acriflavine, Antrycide, pentamidine, stilbamidine) than the standard Crithidia fasciculata, we propose to extend these studies to define media instead of the complex media hiterto used (Goldbery, B. et al., J. Protozool., in press). A defined medium supporting good growth of the Crithidia and Leptomonas has been recently developed by us. We propose to refine this medium to a metabolically minimal medium to make it more sensitive in detecting agents acting as antimetabolites. Since it is desirable that in vitro conditions approach in vivo conditions as closely as practicable, we propose to investigate methods of stabilizing the pH during growth to remain close to blood pH (7.), and to approach blood temperatures as close as possible. The properties of the soluble gamma-glycerophosphate dehydrogenase obtained from the Leptomonas will be examined in more detail especailly its activation by polyamines, as this enzyme appears to have a key regulatory function, and polyamines appear unexplored as targets for chemotherapy.